Fluidized bed spray dryer system

ABSTRACT

A fluidized bed spray drying system for drying liquid into powder including an elongated drying chamber, a spray nozzle assembly at an upper end of the drying chamber and a powder collection chamber at a lower end of the drying chamber. A drying gas inlet is provided in the powder collection chamber and a drying gas outlet is provided at an upper end of the drying chamber. A plurality of cylindrical filter elements at the upper end of the drying chamber are in communication with the exhaust gas outlet for filtering drying gas borne powder from drying gas exiting the drying chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of copending U.S. patentapplication Ser. No. 15/342,710 filed Nov. 3, 2016, a continuation ofcopending U.S. patent application Ser. No. 15/342,726 filed Nov. 3, 2016and a continuation of copending U.S. patent application Ser. No.15/342,742 filed Nov. 3, 2016, all of which claim the benefit of U.S.Patent Application No. 62/250,318 filed Nov. 3, 2015. All of theforegoing applications are incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to spray dryers, and moreparticularly to an apparatus and methods for spray drying liquids intodry powder form.

BACKGROUND OF THE INVENTION

Spray drying is a well known and extensively used process in whichliquid slurries are sprayed into a drying chamber into which heated airis introduced for drying the liquid into powder. The slurry commonlyincludes a liquid, such as water, an ingredient, such as a food, flavor,or pharmaceutical, and a carrier. During the drying process, the liquidis driven off leaving the ingredient in powder form encapsulated withinthe carrier. Spray drying also is used in producing powders that do notrequire encapsulation, such as various food products, additives, andchemicals.

Spray drying systems commonly are relatively massive in construction,having drying towers that can reach several stories in height. Not onlyis the equipment itself a substantial capital investment, the facilityin which it is used must be of sufficient size and design to house suchequipment. Heating requirements for the drying medium also can beexpensive.

While it is desirable to use electrostatic spray nozzles for generatingelectrically charged particles that facilitate quicker drying, due tothe largely steel construction of such sprayer dryer systems, theelectrostatically charged liquid can charge components of the system ina manner, particularly if unintentionally grounded, that can impedeoperation of electrical controls and interrupt operation, resulting inthe discharge of uncharged liquid that is not dried according tospecification.

While it is known to form the drying chamber of electrostatic spraydryers of a non metallic material to better insulate the system from theelectrically charged liquid, particles can adhere to and build up on thewalls of the drying chamber, requiring time consuming cleanup whichinterrupts the use of the system. Moreover, very fine dried powderwithin the atmosphere of heating air in the drying chamber can create adangerous explosive condition from an inadvertent spark or malfunctionof the electrostatic spray nozzle or other components of the system.

Such spray dryer systems also must be operable for spray dryingdifferent forms of liquid slurries. In the flavoring industry, forexample, it may be necessary to operate the system with a citrusflavoring ingredient in one run, while a coffee flavoring ingredient isused in the next operation. Residual flavor material adhering to thewalls of the drying chamber can contaminate the taste of subsequentlyprocessed products. In the pharmaceutical area, of course, it isimperative that successive runs of pharmaceuticals are notcross-contaminated.

Existing spray dryer systems further have lacked easy versatility. Itsometimes is desirable to run smaller lots of a product for drying thatdoes not require utilization of the entire large drying system. Itfurther may be desirable to alter the manner in which material issprayed and dried into the system for particular applications. Still inother processing, it may be desirable that the fine particlesagglomerate during drying to better facilitate ultimate usage, such aswhere more rapid dissolution into liquids with which it is used.Existing sprayers, however, have not lent themselves to easy alterationto accommodate such changes in processing requirements.

Spray dryers further tend to generate very fine particles which canremain airborne in drying gas exiting the dryer system and which must befiltered from gas exiting the system. Such fine particulate matter canquickly clog filters, impeding efficient operation of the dryer andrequiring frequent cleaning of the filters. Existing spray dryers alsohave commonly utilized complex cyclone separation and filterarraignments for removing airborne particulate matter. Such equipment isexpensive and necessitates costly maintenance and cleaning.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spray dryer systemadapted for more efficient and versatile operation.

Another object is to provide a spray dryer system as characterized abovewhich has a filter system for more effectively and efficiently removingairborne particulate matter from drying gas exiting the dryer and withlesser maintenance requirements. A related object is to provide such aspray dryer in which the filter system is effective for enablingrecirculation and reuse of the filtered gases, and particularly inertheating gases.

Another object is to provide a spray dryer system of such type in whichthe drying gas filter system includes means for automatically and moreeffectively removing the buildup of particulate matter on the filters.

A further object is to provide an electrostatic spray dryer system thatis relatively small in size and more reliable in operation.

Still another object is to provide an electrostatic spray dryer systemthat is relatively short in height and can be installed and operated inlocations without special building or ceiling requirements.

A further object is to provide an electrostatic spray dryer system ofthe foregoing type that is effective for spray drying different productlots without cross-contamination.

Yet another object is to provide an electrostatic spray dryer system ofthe above kind that is easily modifiable, both in size and processingtechniques, for particular drying applications.

A further object is to provide an electrostatic spray dryer system thatis operable for drying powders in a manner that enables fine particlesto agglomerate into a form that better facilitates subsequent usage.

Still another object is to provide an electrostatic spray dryer systemthat can be effectively operated with lesser heating requirements, andhence, more economically. A related object is to provide a spray dryersystem of such type that is operable for effectively drying temperaturesensitive compounds.

Another object is to provide a modular electrostatic spray dryer systemin which modules can be selectively utilized for different capacitydrying requirements and which lends itself to repair, maintenance, andmodule replacement without shutting down operation of the spray dryersystem.

Yet another object is to provide an electrostatic spray dryer system ofthe above type that is less susceptible to electrical malfunctions anddangerous explosions from fine powder and the heating atmosphere withinthe drying chamber of the system. A related object is to provide acontrol for such spray dryer system that is effective for monitoring andcontrolling possible electrical malfunctions of the system.

Still a further object is to provide such an electrostatic spray dryersystem that is relatively simple in construction and lends itself toeconomical manufacture.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the powder processing tower of theillustrated spray dryer system;

FIG. 2 is a vertical section of the powder processing tower shown inFIG. 1;

FIG. 3 is an exploded perspective of the illustrated powder processingtower;

FIG. 3A is a plan view of an unassembled flexible non-permeable linerusable with the illustrated powder processing tower;

FIG. 3B is a plan view of an alternative embodiment of a liner similarto that shown in FIG. A1 but made of a permeable filter material;

FIG. 3C is a plan view of another alternative embodiment of liner, inthis case made in part of a non-permeable material and in part of apermeable filter material, usable with the illustrated powder processingtower;

FIG. 3D is a plan view of another alternative embodiment of liner, inthis case made of a non-permeable non-conductive rigid material, usablewith the illustrated powder processing tower;

FIG. 4 is an enlarged top view of the top cap or lid of the illustratedpowder processing tower with an electrostatic spray nozzle centrallysupported therein;

FIG. 5 is a side view of the top cap and spray nozzle assembly shown inFIG. 4;

FIG. 6 is an enlarged vertical section of the illustrated electrostaticspray nozzle assembly;

FIG. 7 is an enlarged fragmentary section of the nozzle supporting headof the illustrated electrostatic spray nozzle assembly;

FIG. 8 is an enlarged fragmentary section of the discharge end of theillustrated electrostatic spray nozzle assembly;

FIG. 8A is a fragmentary section, similar to FIG. 8, showing the spraynozzle assembly with the discharge spray tip altered for facilitatingspraying of more viscous liquids;

FIG. 9 is a transverse section of the illustrated electrostatic spraynozzle assembly taken in the line of 9-9 in FIG. 8;

FIG. 10 is an enlarged fragmentary section of the powder collection coneand filter element housing of the illustrated powder processing tower;

FIG. 10A is an exploded perspective of the powder collection cone andfilter element housing shown in FIG. 10;

FIG. 11 is a side elevational view, in partial section, of analternative embodiment of filter element housing for use with theillustrated powder processing tower;

FIG. 11A is an enlarged fragmentary section of one of the filters of thefilter housing shown in FIG. 11, showing a reverse gas pulse filtercleaning device thereof in an inoperative state;

FIG. 11B is an enlarged fragmentary section, similar to FIG. 11A,showing the reverse gas pulse air filter cleaning device in an operatingcondition;

FIG. 12 is a side elevational view of an alternative embodiment of afilter element housing and powder collection chamber;

FIG. 12A is a top plan view of the filter element housing and powdercollection chamber shown in FIG. 12;

FIG. 12B is an enlarged partial broken away view of the filter elementhousing and powder collection chamber shown in FIG. 12;

FIG. 12C is an exploded perspective of the filter element housing and anassociated upstream air direction plenum shown in FIG. 12;

FIG. 13 is a fragmentary section showing the fastening arrangement forsecuring the top cover to the drying chamber with an associated upperliner standoff ring assembly;

FIG. 13A is a fragmentary section, similar to FIG. 12, but showing thefastening arrangement for securing the drying chamber to the powdercollection cone with an associated bottom liner standoff ring assembly;

FIG. 14 is an enlarged fragmentary view of one of the illustratedfasteners;

FIG. 15 is a schematic of the illustrated spray dryer system;

FIG. 15A is a schematic of an alternative embodiment of a spray dryeroperable for spray chilling of melted flow streams into solidifiedparticles;

FIG. 16 is a fragmentary section showing the fluid supply pump and itsassociated drive motor for the illustrated spray drying system;

FIG. 16A is a vertical section of the illustrated fluid supply pumpsupported within an outer non-conductive housing;

FIG. 17 is an enlarged top view of the illustrated insulting liner andits standoff ring support assembly;

FIG. 18 is an enlarged top view, similar to FIG. 17, but showing astandoff ring assembly supporting a smaller diameter insulating liner;

FIG. 19 is an enlarged side elevational view of the top cap of theillustrated powder processing tower supporting a plurality ofelectrostatic spray nozzle assemblies;

FIG. 20 is a top view of the top cap shown in FIG. 19;

FIG. 21 is a vertical section of the illustrated powder processingtower, modified for supporting the electrostatic spray nozzle centrallyadjacent a bottom of the drying chamber thereof for the upward directionof sprayed liquid for drying;

FIG. 22 is a diagrammatic side elevational view of the bottom mountingsupport of the electrostatic spray nozzle assembly shown in FIG. 21;

FIG. 23 is a top view of the electrostatic spray nozzle assembly andbottom mounting support shown in FIG. 22;

FIG. 24 is an enlarged section of one of the support rods for the spraynozzle bottom mounting support shown in FIGS. 22 and 23;

FIG. 25 is a chart showing alternative configurations for theillustrative powder drying system;

FIG. 25A is a schematic of an alternative embodiment of a spray dryersystem in which fresh nitrogen gas is introduced into the gasrecirculation line of the system;

FIG. 25B is a schematic of another alternative embodiment of a spraydryer system that utilizes a cyclone separator/filter bag assembly forfiltering particulate matter from a recirculating drying gas stream;

FIG. 25C is an alternative embodiment, similar to FIG. 25B, and whichdried line particles separated in the cyclone separator are reintroducedinto the drying chamber;

FIG. 25D is another alternative embodiment of the spray dryer systemthat has a plurality of fluid bed filters for filtering particulatematter from recirculating drying gas;

FIG. 26 is a flowchart for a method of operating a voltage generatorfault recovery method for use in an electrostatic spray dryer system inaccordance with the disclosure;

FIG. 27 is a flowchart for a method of modulating a pulse width in anelectrostatic spray nozzle for use in an electrostatic spray dryersystem in accordance with the disclosure;

FIG. 28 is a top view, diagrammatic depiction of a modular spray dryersystem having a plurality of powder processing towers;

FIG. 29 is a front plan view of the modular spray dryer system shown inFIG. 28; and

FIG. 30 is a top view of the modular spray dryer system, similar to FIG.28, but having additional powder processing towers.

While the invention is susceptible of various modifications andalternative constructions, certain illustrative embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific forms disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to the drawings, there is shown anillustrative spray drying system 10 in accordance with the inventionwhich includes a processing tower 11 comprising a drying chamber 12 inthe form of an upstanding cylindrical structure, a top closurearrangement in the form of a cover or lid 14 for the drying chamber 12having a heating air inlet 15 and a liquid spray nozzle assembly 16, anda bottom closure arrangement in the form of a powder collection cone 18supported at the bottom of the drying chamber 12, a filter elementhousing 19 through which the powder collection cone 18 extends having aheating air exhaust outlet 20, and a bottom powder collection chamber21. The drying chamber 12, collection cone 18, filter element housing19, and powder collection chamber 21 all preferably are made ofstainless steel. The top cover 14 preferably is made of plastic or othernonconductive material and in this case centrally supports the spraynozzle assembly 16. The illustrated heating air inlet 15 is oriented fordirecting heated air into the drying chamber 12 in a tangential swirlingdirection. A frame 24 supports the processing tower 11 in uprightcondition.

Pursuant to an important aspect of this embodiment, the spray nozzleassembly 16, as best depicted in FIGS. 6-9, is a pressurized airassisted electrostatic spray nozzle assembly for directing a spray ofelectrostatically charged particles into the dryer chamber 12 for quickand efficient drying of liquid slurries into desired powder form. Theillustrated spray nozzle assembly 16, which may be of a type disclosedin the International application PCT/US2014/056728, includes a nozzlesupporting head 31, an elongated nozzle barrel or body 32 extendingdownstream from the head 31, and a discharge spray tip assembly 34 at adownstream end of the elongated nozzle body 32. The head 31 in this caseis made of plastic or other non conductive material and formed with aradial liquid inlet passage 36 that receives and communicates with aliquid inlet fitting 38 for coupling to a supply line 131 thatcommunicates with a liquid supply. It will be understood that the supplyliquid may be any of a variety of slurries or like liquids that can bedried into powder form, including liquid slurries having a solvent, suchas water, a desired ingredient, such as a flavoring, food, apharmaceutical, or the like, and a carrier such that upon drying intopowder form the desired ingredient is encapsulated within the carrier asknown in the art. Other forms of slurries may also be used includingliquids that do not include a carrier or require encapsulation of thedried products.

The nozzle supporting head 31 in this case further is formed with aradial pressurized air atomizing inlet passage 39 downstream of saidliquid inlet passage 36 that receives and communicates with an air inletfitting 40 coupled to a suitable pressurized gas supply. The head 31also has a radial passage 41 upstream of the liquid inlet passage 36that receives a fitting 42 for securing a high voltage cable 44connected to a high voltage source and having an end 44 a extending intothe passage 41 in abutting electrically contacting relation to anelectrode 48 axially supported within the head 31 and extendingdownstream of the liquid inlet passage 36.

For enabling liquid passage through the head 31, the electrode 48 isformed with an internal axial passage 49 communicating with the liquidinlet passage 36 and extending downstream though the electrode 48. Theelectrode 48 is formed with a plurality of radial passages 50communicating between the liquid inlet passage 36 and the internal axialpassage 49. The illustrated electrode 48 has a downstream outwardlyextending radial hub 51 fit within a counter bore of the head 31 with asealing o-ring 52 interposed there between.

The elongated body 32 is in the form of an outer cylindrical body member55 made of plastic or other suitable nonconductive material, having anupstream end 55 a threadably engaged within a threaded bore of the head31 with a sealing o-ring 56 interposed between the cylindrical bodymember 55 and the head 31. A liquid feed tube 58, made of stainlesssteel or other electrically conductive metal, extends axially throughthe outer cylindrical body member 55 for defining a liquid flow passage59 for communicating liquid between the axial electrode liquid passage49 and the discharge spray tip assembly 34 and for defining an annularatomizing air passage 60 between the liquid feed tube 58 and the outercylindrical body member 55. An upstream end of the liquid feed tube 58which protrudes above the threaded inlet end 55 a of the outercylindrical nozzle body 55 fits within a downwardly opening cylindricalbore 65 in the electrode hub 51 in electrical conducting relation. Withthe electrode 48 charged by the high voltage cable 44, it will be seenthat liquid feed to the inlet passage 36 will be electrically chargedduring its travel through the electrode passage 49 and liquid feed tube58 along the entire length of the elongated nozzle body 32. Pressurizedgas in this case communicates through the radial air inlet passage 39about the upstream end of the liquid feed tube 58 and then into theannular air passage 60 between the liquid feed tube 58 and the outercylindrical body member 55.

The liquid feed tube 58 is disposed in electrical contacting relationwith the electrode 48 for efficiently electrically charging liquidthroughout its passage from the head 31 and through elongated nozzlebody member 32 to the discharge spray tip assembly 34. To that end, thedischarge spray tip assembly 34 includes a spray tip 70 having anupstream cylindrical section 71 in surrounding relation to a downstreamend of the liquid feed tube 58 with a sealing o-ring 72 interposedtherebetween. The spray tip 70 includes an inwardly tapered or conicalintermediate section 74 and a downstream cylindrical nose section 76that defines a cylindrical flow passage 75 and a liquid dischargeorifice 78 of the spray tip 70. The spray tip 70 in this case has asegmented radial retention flange 78 extending outwardly of the upstreamcylindrical section 71 which defines a plurality of air passages 77, aswill become apparent.

For channeling liquid from feed tube 58 into and though the spray tip 70while continuing to electrostatically charge the liquid as it isdirected through the spray tip 70, an electrically conductive pin unit80 is supported within the spray tip 70 in abutting electricallyconductive relation to the downstream end of the feed tube 58. The pinunit 80 in this case comprises an upstream cylindrical hub section 81formed with a downstream conical wall section 82 supported within theintermediate conical section 74 of the spray tip 70. The cylindrical hubsection 81 is formed with a plurality of circumferentially spaced radialliquid flow passageways 83 (FIG. 8) communicating between the liquidfeed tube 58 and the cylindrical spray tip passage section 75. It willbe seen that the electrically conductive pin unit 80, when seated withinthe spray tip 70, physically supports in abutting relation thedownstream end of the liquid feed tube 58.

For concentrating the electrical charge on liquid discharging from thespray tip, the pin unit 80 has a downwardly extending central electrodepin 84 supported in concentric relation to the spray tip passage 75 suchthat the liquid discharge orifice 78 is annularly disposed about theelectrode pin 84. The electrode pin 84 has a gradually tapered pointedend which extends a distance, such as between about ¼ and ½ inch, beyondthe annular spray tip discharge orifice 78. The increased contact of theliquid about the protruding electrode pin 84 as it exits the spray tip70 further enhances concentration of the charge on the dischargingliquid for enhanced liquid particle breakdown and distribution.

Alternatively, as depicted in FIG. 8A, when spraying more viscousliquids, the discharge spray tip assembly 34 may have a hub section 81,similar to that described above, but without the downwardly extendingcentral electrode pin 84. This arrangement provides freer passage of themore viscous liquid through the spray tip, while the electrostaticcharge to discharging liquid still enhances liquid breakdown for moreefficient drying of such viscous liquids.

The discharge spray tip assembly 34 further includes an air or gas cap90 disposed about the spray tip 70 which defines an annular atomizingair passage 91 about the spray tip 70 and which retains the spray tip70, pin unit 80, and liquid feed tube 58 in assembled conductiverelation to each other. The air cap 90 in this instance defines aconical pressurized air flow passage section 91 a about the downstreamend of the spray tip 70 which communicates via the circumferentiallyspaced air passages 77 in the spray tip retention flange 78 with theannular air passage 60 between the liquid feed tube 58 and the outercylindrical body member 55 for directing a pressurized air or gasdischarge stream through an annular discharge orifice 93 about the spraytip nose 76 and liquid discharging from the spray tip liquid dischargeorifice 78. For retaining the internal components of the spray nozzle inassembled relation, the air cap 90 has an upstream cylindrical end 95 inthreaded engagement about a downstream outer threaded end of the outercylindrical member 55. The air cap 90 has a counter bore 96 whichreceives and supports the segmented radial flange 78 of the spray tip 70for supporting the spray tip 70, and hence, the pin unit 80 and liquidfeed tube 58 in electrical conducting relation with the upstreamelectrode 48.

The spray nozzle assembly 16 is operable for discharging a spray ofelectrostatically charged liquid particles into the drying chamber 12.In practice, it has been found that the illustrated electrostatic spraynozzle assembly 16 may be operated to produce extremely fine liquidparticle droplets, such as on the order of 70 micron in diameter. Aswill become apparent, due to the breakdown and repelling nature of suchfine liquid spray particles and heated drying gas introduced into thedrying chamber, both from the heating air inlet 15 and the air assistedspray nozzle assembly 16, the liquid particles are susceptible to quickand efficient drying into fine particle form. It will be understood thatwhile the illustrated electrostatic spray nozzle assembly 16 has beenfound to have particular utility in connection with the subjectinvention, other electrostatic spray nozzles and systems could be used,including electrostatic hydraulic rotary spray nozzles and high volumelow pressure electrostatic spray nozzles of known types.

Pursuant to a further important feature of the present embodiment, thedrying chamber 12 has an internal non-metallic insulating liner 100disposed in concentric spaced relation to the inside wall surface 12 aof the drying chamber 12 into which electrostatically charged liquidspray particles from the spray nozzle assembly 16 are discharged. Asdepicted in FIG. 2, the liner has a diameter d less than the internaldiameter dl of the drying chamber 12 so as to provide an insulating airspacing 101, preferably at least about 2 inches (about 5 cm), with theouter wall surface 12 a of the drying chamber 12, but other dimensionsmay be used. In this embodiment, the liner 100 is non-structuralpreferably being made of a non-permeable flexible plastic material 100 a(FIGS. 3 and 3A). Alternatively, as will become apparent, it may be madeof a rigid non-permeable non-conductive material 100 c (FIG. 3D), apermeable filter material 100 b (FIG. 3B), or in part a non-permeablematerial 100 a and in part a permeable filter material 100 b (FIG. 3C).

According to another aspect of the present embodiment, the processingtower 11 has a quick disconnect assembled construction that facilitatesassembly and the mounting of the annular liner 100 in electricallyinsulated relation to the outer wall of the drying chamber 12. To thisend, the annular insulating liner 100 is supported at opposite ends byrespective upper and lower standoff ring assemblies 104 (FIGS. 1, 3, 13,13A, 14 and 17). Each ring assembly 104 in this case includes an innercylindrical standoff ring 105 to which an end of the liner 100 isattached and a plurality of circumferentially spaced non-conductive,polypropylene or other plastic, standoff studs 106 fixed in outwardlyextended radial relation to the standoff ring 105. In the illustratedembodiment, the upper end of the liner 100 is folded over the top of thestandoff ring 105 of the upper ring assembly 104 and affixed thereto byan annular U configured rubber gasket 108 positioned over the folded endof the liner 100 and the standoff ring 105 (FIG. 13). The lower end ofthe liner 100 is similarly trained about the bottom of the standoff ring105 of the lower ring assembly 104 and secured thereto by a similarrubber gasket 108 (FIG. 13). Similar rubber gaskets 108 also aresupported on the opposite inner ends of the cylindrical standoff rings105 of the ring assemblies 104 for protecting the liner 100 from damageby exposed edges of the standoff rings 105.

For securing each standoff ring assembly 104 within the drying chamber12, a respective mounting ring 110 is affixed, such as by welding, to anouter side of the drying chamber 12. Stainless steel mounting screws 111extend through aligned apertures in the mounting ring 110 and outer wallof the drying chamber 12 for threadably engaging the insulating standoffstuds 106. A rubber o-ring 112 in this instance is provided about theend of each standoff stud 106 for sealing the inside wall of the dryingchamber 12, and a neoprene bonded sealing washer 114 is disposed aboutthe head of each retaining screw 111.

For securing the drying chamber top cover 14 in place on the dryingchamber 12 in sealed relation to the upper standoff ring assembly 104,an annular array 120 (FIGS. 1 and 2) spaced releasable latch assemblies121 are secured to the mounting ring 110 (FIGS. 13-14) atcircumferentially spaced locations intermediate the standoff studs 106.The latch assemblies 121 may be of a known type having an upwardlyextending draw hook 122 positionable over a top marginal edge of thecover 14 and drawn down into a locked position as an incident todownward pivotal movement of a latch arm 124 into a latching positionfor retaining the top cover 14 against the U-shaped gasket 108 about theupper edge of the standoff ring 105 and a similar large diameter annularU shaped gasket 126 about an upper edge of the cylindrical dryingchamber 12. The latch assemblies 121 may be easily unlatched by reversepivotal movement of the latch hooks 124 to move the draw hooks 122upwardly and outwardly for permitting removal of the top cover 14 whennecessary. A similar annular array 120 a of latch assemblies 121 isprovided about a mounting ring 110 adjacent the bottom of the dryingchamber 12, in this case having draw hooks 124 positioned downwardlyinto overlying relation with an outwardly extending flange 129 of thecollection cone 18 for retaining the flange 129 of the collection cone18 in sealed relation with rubber gaskets 108, 126 about the bottom edgeof the standoff ring 105 and the bottom cylindrical edge of the dryingchamber 12 (FIG. 13A). It will be understood that for particularapplications the liner 100, o-rings and other sealing gaskets 108,126may or may not be made of FDA compliant materials.

During operation of the electrostatic spray nozzle assembly 16, liquidsupplied to the electrostatic spray nozzle assembly 16 from a liquidsupply, which in this case is a liquid holding tank 130 as depicted inFIG. 15, is directed by the electrostatic spray nozzle assembly 16 intoan effective drying zone 127 defined by the annular liner 100. Liquid issupplied from the liquid supply holding tank 130 through a liquid supplyor delivery line 131 connected to the liquid inlet fitting 38 of thespray nozzle assembly 16 via a pump 132, which preferably is aperistaltic dosing pump having a liquid directing roller system operablein a conventional manner. The peristaltic dosing pump 132 in this case,as depicted in FIG. 16A, comprises three plastic electrically isolatedpump rollers 33 within a plastic pump housing 37. The liquid supply ordelivery line 131 in this case is an electrically shielded tubing, andthe stainless steel drying chamber 12 preferably is grounded by anapproved grounding line through the support frame 24 to which it issecured with metal to metal contact.

An electronic controller 133 is operably connected to the variousactuators and electric or electronic devices of the electrostatic spraydryer system such as an electric motor 134, the pump 132, the liquidspray nozzle assembly 16, a high voltage generator providing electricalvoltage to the high voltage cable 44, and others, and operates tocontrol their operation. While a single controller is shown, it shouldbe appreciated that a distributed controller arrangement including morethan one controller can be used. As shown, the controller 133 is capableof operating in response to a program such as a programmable logiccontroller. The various operable connections between the controller 133and the various other components of the system are omitted from FIG. 15for clarity.

Pursuant to a further aspect of the present embodiment, the pump 132 isoperated by the electric motor 134 (FIG. 16) disposed in electricallyisolated relation to the pump 132 and the liquid supply line 131coupling the pump 132 to the spray nozzle assembly 16 for preventing anelectrical charge to the motor 134 from liquid electrostatically chargedby the spray nozzle assembly 16. To that end, the drive motor 134 has anoutput shaft 135 coupled to a pump head drive shaft 136 by anon-electrically conductive drive segment 138, such as made of a rigidnylon, which isolates the pump 132 from the electric drive motor 134.The nonconductive drive segment 138 in the illustrated embodiment has adiameter of about 1.5 inches (about 3.8 cm) and an axial length of about5 inches (about 12.7 cm). The electric motor drive shaft 135 in thiscase carriers an attachment plate 139 which is fixed to thenonconductive drive segment 138 by screws 141. The pump head drive shaft136 similarly carries an attachment plate 140 affixed by screws 141 tothe opposite end of the nonconductive drive segment 138.

An electrostatic voltage generator 222 is electrically connected to thenozzle assembly 16 via an electrical line 224 for providing a voltagethat electrostatically charges the sprayed liquid droplets. In theillustrated embodiment, the electrical line 224 includes a variableresistor element 226, which is optional and which can be manually orautomatically adjusted to control the voltage and current provided tothe spray nozzle assembly 16. An optional grounding wire 228 is alsoelectrically connected between the liquid supply line 131 and a ground232. The grounding wire 228 includes a variable resistor 230 that can bemanually or automatically adjusted to control a voltage that is presentin the fluid. In the illustrated embodiment, the grounding wire isplaced before the pump 132 to control the electrical charge state of thefluid provided to the system. The system may further include sensorscommunicating the charged state of the fluid to the controller 133 suchthat the system may automatically monitor and selectively control thecharge state of the liquid by controlling the resistance of the variablegrounding resistor 230 to bleed charge off from the liquid line in thesystem.

The drive motor 134, which also is appropriately grounded, in thisinstance is supported within a nonconductive plastic motor mountinghousing 144. The illustrated liquid holding tank 130 is supported on aliquid scale 145 for enabling monitoring the amount of liquid in thetank 130, and an electrical isolation barrier 146 is provided betweenthe underside of the liquid holding tank 130 and the scale 145. It willbe understood that in lieu of the peristaltic pump 132, plastic pressurepots and other types of pumps and liquid delivery systems could be usedthat can be electrically insulated from their electrical operatingsystem.

Pressurized gas directed to the atomizing air inlet fitting 18 of thespray nozzle assembly 16 in this case originates from a bulk nitrogensupply 150 which communicates with the atomizing air inlet fitting 18 ofthe spray nozzle assembly 16 via a gas supply line 151 (FIG. 15). A gasheater 152 is provided in the supply line 151 for enabling dry inertnitrogen gas to be supplied to the spray nozzle assembly 16 at acontrolled temperature and pressure. It will be understood that whilenitrogen is described as the atomizing gas in connection with thepresent embodiment, other inert gases could be used, or other gasseswith air could be used so long as the oxygen level within the dryingchamber is maintained below a level that would create a combustiveatmosphere with the dry powder particles within the drying chamber thatis ignitable from a spark or other electrical malfunction of theelectrostatic spray nozzle assembly or other electronically controlledelements of the drying system.

Pursuant to a further important aspect of the present embodiment, heatednitrogen atomizing gas supplied to the spray nozzle assembly 16 anddirected into the drying chamber 12 as an incident to atomization ofliquid being sprayed into the drying chamber 12 is continuouslyrecirculated through the drying chamber 12 as the drying medium. As willbe understood with further reference to FIG. 15, drying gas introducedinto the drying chamber 12 both from the drying gas inlet 15 and thespray nozzle assembly 16 will circulate the length of the drying chamber12 efficiently drying the electrostatically charged liquid particlessprayed into the drying chamber 12 into powder form. The dried powderwill migrate through the powder collection cone 18 into the powdercollection chamber 21, where it can be removed by appropriate means,either manually or by other automated means.

The illustrated powder collection cone 18, as best depicted in FIGS. 10and 10A, has an upper cylindrical section 155, an inwardly taperedconical intermediate section 156, and a lower cylindrical powderdelivery section 158 that extends centrally through the filter elementhousing 19 for channeling dried powder into the powder collectionchamber 21. The filter element housing 19 in this case has a pair ofvertically stacked annular HEPA filters 160 mounted in surroundingoutwardly spaced relation to the lower sections of the powder collectioncone 18. The illustrated powder collection cone 18 has an outwardlyextending radial flange 161 intermediate its ends positioned over theupper filter 160 in the filter element housing 19 with an annular seal162 interposed between the radial flange 161 and the filter elementhousing 19. While the bulk of the dried powder will fall downwardlythrough the collection cone 18 into the powder collection chamber 19,only the finest particles will remain entrained in the drying gas as itmigrates upwardly around the bottom sections of the powder collectioncone 18 and then outwardly through the HEPA filters 160 which restrainand filter out the fine powder, prior to exiting through the exhaust gasoutlet 20 of the filter housing 19.

Alternatively, as depicted in FIGS. 11, 11A and 11B, a filter elementhousing 19 a may be used that comprises a plurality of circumferentiallyspaced cylindrical filters 160 a that are mounted in depending verticalrelation from an intermediate transverse support panel 163 of a housing19 a. Gas latent with powder particles directed from the collection cone18 into a lower collection chamber flows transversely through thefilters 160 a into a common exhaust plenum 164 within the filter elementhousing 19 a above the transverse support panel 163 for communicationthrough an outlet port 20 a with the particles being restricted from theair flow by the filters 160 a. For periodically cleaning the filters 160a, the filters 160 a each have a respective reverse pulse air filtercleaning device 167 of a type disclosed in U.S. Pat. No. 8,876,928assigned to the same applicant as the present application, thedisclosure of which is incorporated herein by reference. Each of thereverse pulse air filter cleaning devices 167 has a respective gassupply line 167 a for coupling to a pulsed air supply.

The illustrated the reverse pulse air filter cleaning devices 21, asdepicted in FIGS. 11A and 11B, each includes a reverse pulse nozzle 240having a gas inlet 241 in an upper wall of the exhaust plenum 164 fixedby an annular retainer 242 for connection to the compressed gas supplyline 167 a coupled to a pressurized gas source, such as nitrogen. Thenozzle 240 has a cylindrical closed bottom construction which defines ahollow inner air passageway 244 extending from the inlet 241 through theexhaust plenum 164 and substantially the length of the filter 160 a. Thenozzle 240 is formed with a plurality of relatively large diameterdischarge holes 246 in a section within the exhaust plenum 164 and aplurality of smaller sized air discharge holes 248 in the length of thenozzle 240 within the filter 160 a.

For interrupting the flow of process gas from the filter element housing19 a to the exhaust plenum 164 during operation of the reverse pulsenozzle 240, an annular exhaust port cut off plunger 249 is disposedabove the reverse pulse nozzle 160 a for axial movement within theexhaust plenum 164 between exhaust port opening and closing positions.For controlling movement of the plunger 249, a bottom opening plungercylinder 250 is mounted in sealed depending relation from the upper wallof the exhaust plenum 164. The illustrated plunger 249 includes an upperrelatively small diameter annular sealing and guide flange 252 having anouter perimeter adapted for sliding sealing engagement with the interiorof the cylinder 250 and a lower larger diameter valve head 254 disposedbelow the lower terminal end of the cylinder 250 for sealing engagementwith an exhaust port 253 in the panel 163. The plunger 249 preferably ismade of a resilient material, and the upper sealing and guide flange 252and lower valve head 254 have downwardly tapered or cup shapedconfigurations.

The plunger 249 is disposed for limited axial movement along the reversepulse nozzle 240 and is biased to a normally open or retracted position,as shown in FIG. 3, by coil spring 256 fixed about the outer perimeterof the reverse pulse nozzle 240. With the valve plunger 249 biased tosuch position, process gas flows from the filter element housing 19 athrough the filter 160 a, exhaust port 253 and into the exhaust plenum164.

During a reverse pulse gas cleaning cycle, a pulse of compressed gas isdirected through the reverse pulse nozzle 240 from the inlet line 167 a.As the compressed gas travels through the nozzle 160 a, it first isdirected through the larger diameter or plunger actuation holes 246 intothe plunger cylinder 250 above the plunger sealing and guide flange 252and then though the smaller reverse pulse nozzle holes 248. Since thelarger holes 249 provide the path of less resistance, gas first flowsinto the plunger cylinder 250 and as pressure in the plunger cylinder250 increases, it forces the plunger 249 downwardly against the biasingforce of the spring 256. Eventually, the pressure builds to a pointwhere it overcomes the force of the spring 256 and forces the plunger249 downwardly toward the exhaust port 253 temporarily sealing it off.After the plunger 249 seals the exhaust port 253 the compressed gas inthe outer plunger cylinder 250 can no longer displace the plunger 249and gas pressure in the plunger cylinder 250 increases to a point thatthe compressed gas is then forced through the smaller nozzle holes 248and against the filter 160 a for dislodging build up particulate matterabout its outside surface.

Following the reverse compressed air pulse and the dislodgement of theaccumulated particulate on the filter 160 a, pressure will dissipatewithin the plunger cylinder 250 to the extent that it will no longercounteract the spring 256. The plunger 249 then will move upwardly underthe force of the spring 256 to its retracted or rest position, unsealingthe exhaust port 253 for continued operation of the dryer.

Still another alternative embodiment of an exhaust gas filter elementhousing 270 and powder collection chamber 271 mountable on a lower endof the drying chamber 12 is depicted FIGS. 12-12B. In this case, anupper powder direction plenum 272 is mountable on an underside of theelongated drying chamber 12, the filter element housing 270 includes aplurality of vertically oriented cylindrical filters 274 and is disposedbelow the powder direction plenum 272, a powder direction cone 275 iscoupled to the underside of the filter element housing 270, and thepowder collection chamber 271 is supported on an underside of the powderdirection cone 275.

The illustrated powder direction plenum 272 comprises an outercylindrical housing wall 289 mountable in sealed relation to anunderside of the drying chamber 12 and having an open upper end forreceiving drying gas and powder from the drying chamber 12 and dryingzone 127. Housed within the powder direction plenum 272 is a downwardlyopening conically configured exhaust plenum 281 which defines on itsunderside an exhaust chamber 282 (FIG. 12B) and on its upper sidedirects drying gas and powder from the drying chamber 12 downwardly andoutwardly around an outer perimeter of the conical exhaust plenum 281.

The filter element housing 270 comprises an outer cylindrical housingwall 284 mounted in sealed relation by means of an annular seal 285 to abottom peripheral edge of the powder direction plenum 272 and an innercylindrical filter shroud 286 mounted in sealed relation by means of anannular seal 288 to the bottom peripheral edge of the conical exhaustplenum 281. The conical exhaust plenum 281 and the inner cylindricalfilter shroud 286 are supported within an outer cylindrical housing wall289 of the gas directing plenum 272 and filter element housing 270 bythe plurality of radial supports 290 (FIG. 12A) so as to define airpassageways 291 communicating about the bottom perimeter of the conicalexhaust plenum 281 and an annular gas passageway 292 between the innercylindrical filter shroud 286 and outer cylindrical housing wall 284such that gas and powder passing through the powder direction plenum 272is directed by the conical exhaust plenum 281 outwardly about the filterelement shroud 281 into the underlying powder direction cone 275 andcollection chamber 271.

The cylindrical filters 274 in this case are supported in dependingrelation to a circular support plate 295 fixedly disposed below theunderside of the downwardly opening conical exhaust plenum 281. Thecircular filter support plate 295 in this case is mounted in slightlyrecessed relation to an upper perimeter of the cylindrical shroud 286and defines a bottom wall of the exhaust chamber 282. The illustratedcylindrical filters 274 each are in cartridge form comprising acylindrical filter element 296, an upper cylindrical cartridge holdingplate 298, a bottom end cap and sealing plate 299 with interposedannular sealing elements 300, 301, 302. For securing the filtercartridges in assembled relation, the upper cartridge holding plate 298has a depending U-shaped support member 304 with a threaded lower endstud 305 positionable through a central aperture in the bottom end cap299 which is secured by a nut 306 with a o-ring sealing ring 308interposed therebetween. The upper holding plate 298 of each filtercartridge is fixed in sealed relation about a respective circularopening 310 in the central support plate 295 with the filter element 296disposed in depending relation to an underside of the support plate 295and with a central opening 311 in the holder plate 298 communicatingbetween the exhaust chamber 282 and the inside of the cylindrical filterelement 296. The filter element cartridges in this case are disposed incircumferentially spaced relation about a center of the inner shroud274.

The filter element housing 270 in this instance is secured to the powderdirection plenum 272 by releasable clamps 315 or like fasteners topermit easy access to the filter cartridges. The inner filter shroud 286also is releasably mounted in surrounding relation to the cylindricalfilters 274, such as by a pin and slot connection, for enabling accessto the filters for replacement.

During operation of the dryer system, it will be seen that drying gasand powder directed into the powder direction plenum 272 will bechanneled about the conical exhaust plenum 281 into the annularpassageways 291, 292 about the inner filter element shroud 274downwardly into the powder direction cone 275 and collection chamber 271for collection in the chamber 271. While most of the dried powderremaining in the gas flow will migrate into the powder collectionchamber 271, as indicated previously, fine gas borne particulate matterwill be separated and retained by the annular filters 274 as the dryinggas passes through the filters into the drying gas exhaust plenum 282for exit through a drying gas exhaust port 320 and recirculation to thedrying chamber 12, as will be become apparent.

For cleaning the cylindrical filters 274 of buildup of powder during thecourse of usage of the dryer system, the cylindrical filters 274 eachhave a respective reverse gas pulse cleaning device 322. To this end,the gas direction plenum 272 in this case has an outer annularpressurized gas manifold channel 321 coupled to a suitable pressurizedair supply. Each reverse air pulse cleaning device 322 has a respectivepressurized gas supply line 325 coupled between the annular pressurizedgas manifold channel 321 and a respective control valve 326, which inthis case mounted on an outer side of the air direction plenum 272. Agas pulse direction line or tube 328 extends from the control valve 326radially through the air direction plenum 272 and the conical wall ofthe exhaust plenum 329 and then with a right angle turn downwardly witha terminal discharge end 329 of the gas pulse directing line 328disposed above and in aligned relation to the the central opening 311 ofthe filter cartridge holding plate 298 and underlying cylindrical filterelement 296.

By appropriate selective or automated control of the control valve 326,the control valve 26 can be cyclically operated to discharge pulses ofthe compressed gas from the line 328 axially into the cyclical filter274 for dislodging accumulated powder on the exterior wall of thecylindrical filter element 296. The discharge end 329 of the pulse gasdirecting line 328 preferably is disposed in spaced relation to an upperend of the cyclical filter 274 to facilitate the direction of compressedgas impulses into the filter element 296 while simultaneously drawing ingas from the exhaust chamber 282 which facilitates reverse flow impulsesthat dislodge accumulated powder from the filter element 296. Preferablythe discharge end 329 of the air tube 328 is spaced a distance away fromthe upper end of the cylindrical filter element such that the expandingair flow, depicted as 330 in FIG. 12B, upon reaching the filtercartridge, has an outer perimeter corresponding substantially to thediameter of the central opening 311 in the cartridge holding plate 298.In the exemplary embodiment, the air direction tube 28 has a diameter ofabout one inch and the discharge end 329 is spaced a distance of abouttwo and a half inches from the holding plate 298.

The powder collection chamber 271 in this case has a circular butterflyvalve 340 (shown in FIG. 12B in breakaway fashion within the powdercollection chamber 271) mounted at an upper end of the collectionchamber 271 operable by a suitable actuating device 341 for rotatablemovement between a vertical or open position which allows dried powderto be directed into the collection chamber 271 and a horizontal closedposition which blocks the passage of dried powder into the collectionchamber 271 when powder is being removed. Alternatively, it will beunderstood that the powder collection chamber 271 could deposit powderdirectly onto a moveable conveyor from an open bottom end.

For enabling recirculation and reuse of the exiting drying gas from thefilter element housing 19 a, the exhaust outlet 20 of the filter housing19 is coupled to a recirculation line 165 which in turn is connected tothe heating gas inlet port 15 of the top cover 14 of the heating chamber12 through a condenser 166, a blower 168, and a drying gas heater 169(FIG. 15). The condenser 170 removes any water vapor from the exhaustgas flow stream by means of cold water chilled condensing coils 170 ahaving respective cold water supply and return lines 171, 172.Condensate from the condenser 170 is directed to a collection container174 or to a drain. Dried nitrogen gas is then directed by the blower 168through the gas heater 169 which reheats the drying gas after cooling inthe condenser 170 to a predetermined heated temperature for theparticular powder drying operating for redirection back to the heatinggas inlet port 15 and into the heating chamber 12. An exhaust controlvalve 175 coupled to the recirculation line 165 between the blower 168and the heater 169 allows excess nitrogen gas introduced into the systemfrom the electrostatic spray nozzle assembly 16 to be vented to anappropriate exhaust duct work 176. The exhaust flow from the controlvalve 175 may be set to match the excess nitrogen introduced into thedrying chamber 12 by the electrostatic spray nozzle assembly 16. It willbe appreciated that by selective control of the exhaust flow controlvalve 175 and the blower 168 a vacuum or pressure level in the dryingchamber 12 can be selectively controlled for particular dryingoperations or for the purpose of controlling the evaporation and exhaustof volatiles. While a cold water condenser 170 has been shown in theillustrated embodiment, it will be understood that other types ofcondensers or means for removing moisture from the recirculating gasflow stream could be used.

It will be appreciated that the drying gas introduced into the effectivedrying zone 127 defined by the flexible liner 100 both from theelectrostatic spray nozzle assembly 16 and the drying gas inlet port 15,is a dry inert gas, i.e. nitrogen in the illustrated embodiment, thatfacilitates drying of the liquid particles sprayed into the dryingchamber 12 by the electrostatic spray nozzle assembly 16. Therecirculation of the inert drying gas, as described above, also purgesoxygen from the drying gas so as to prevent the chance of a dangerousexplosion of powder within the drying chamber in the event of anunintended spark from the electrostatic spray nozzle assembly 16 orother components of the system.

Recirculation of the inert drying gas through the spray drying system10, furthermore, has been found to enable highly energy efficientoperation of the spray drying system 10 at significantly lower operatingtemperatures, and correspondingly, with significant cost savings. Asindicated previously, emulsions to be sprayed typically are made ofthree components, for example, water (solvent), starch (carrier) and aflavor oil (core). In that case, the object of spray drying is to formthe starch around the oil and dry off all of the water with the dryinggas. The starch remains as a protective layer around the oil, keeping itfrom oxidizing. This desired result has been found to be more easilyachieved when a negative electrostatic charge is applied to the emulsionbefore and during atomization.

While the theory of operation is not fully understood, each of the threecomponents of the sprayed emulsion has differing electrical properties.Water being the most conductive of the group, will easily attract themost electrons, next being the starch, and finally oil being the mostresistive barely attracts electrons. Knowing that opposite chargesattract and like charges repel, the water molecules, all having thegreatest like charge, have the most repulsive force with respect to eachother. This force directs the water molecules to the outer surface ofthe droplet where they have the greatest surface area to the drying gaswhich enhances the drying process. The oil molecules having a smallercharge would remain at the center of the droplet. It is this processthat is believed to contribute to more rapid drying, or drying with alower heat source, as well as to more uniform coating. Testing of thespray dried powder produced by the present spray drying system operatedwith an inlet drying gas temperature of 90 degrees C. found the powdercomparable to that dried in conventional spray drying processes operableat 190 degrees C. Moreover, in some instances, the subject spray dryingsystem can be effectively operated without heating of the drying gas.

Encapsulation efficiency, namely the uniformity of the coating of thedried powder, also was equal to that achieved in higher temperaturespray drying. It further was found that lower temperature dryingsignificantly reduced aromas, odors and volatile components dischargedinto the environment as compared to conventional spray drying, furtherindicating that the outer surface of the dried particle was moreuniformly and completely formed of starch. The reduction of dischargingaromas and odors further enhances the working environment and eliminatesthe need for purging such odors that can be irritating and/or harmful tooperating personnel. Lower temperature processing also enables spraydrying of temperature sensitive components (organic or inorganic)without damage or adversely affecting the compounds.

If during a drying process any particles may stick or otherwiseaccumulate on the surface of the liner 100, a liner shaking device isprovided for periodically imparting shaking movement to the liner 100sufficient to remove any accumulated powder. In the illustratedembodiment, the drying chamber 12 has a side pneumatic liner shake valveport 180 which is coupled to a pneumatic tank 181 that can beperiodically actuated to direct pressurized air through the pneumaticliner shake valve port 180 and into the annular air space between theliner 100 and the outer wall of the drying chamber 12 that shakes theflexible liner 100 back and forth with sufficient force to dislodge anyaccumulated powder. Pressurized air preferably is directed to thepneumatic liner shake valve port 180 in a pulsating manner in order toaccentuate such shaking motion. Alternatively, it will be understoodthat mechanical means could be used for shaking the liner 100.

In order to ensure against cross contamination between successivedifferent selective usage of the spray dryer system, such as betweenruns of different powders in the drying chamber 12, the annular arrays120, 120 a of quick disconnect fasteners 121 enable disassembly of thecover 14 and collection cone 18 from the drying chamber 12 for easyreplacement of the liner 100. Since the liner 100 is made of relativelyinexpensive material preferably it is disposable between runs ofdifferent powders, with replacement of a new fresh replacement linerbeing affected without undue expense.

In keeping with another important feature of this embodiment, the dryingchamber 12 is easily modifiable for different spray drying requirements.For example, for smaller drying requirements, a smaller diameter liner100 a may be used to reduce the size of the effective drying zone. Tothat end, standoff ring assemblies 104 a (FIG. 18), similar to thatdescribed above, but with a smaller diameter inner standoff rings 105 a,can be easily substituted for the larger diameter standoff ring assembly104. The substitution of the ring assemblies may be accomplished byunlatching the circumferentially spaced arrays 120, 120 a of latches 121for the top cover 14 and collection cone 18, removing the largerdiameter ring assemblies 104 from the drying chamber 12, replacing themwith the smaller diameter ring assemblies 104 a and liner 100 a, andreassembling and relatching the top cover 14 and collection cone 18 ontothe drying chamber 12. The smaller diameter liner 100 a effectivelyreduces the drying zone into which heated drying gas and atomizing gasis introduced for enabling both quicker and more energy efficientsmaller lot drying.

In further enabling more efficient drying of smaller lot runs, thedrying chamber 12 has a modular construction that permits reducing thelength of the drying chamber 12. In the illustrated embodiment, thedrying chamber 12 comprises a plurality, in this case two, verticalstacked cylindrical drying chamber modules or sections 185, 186. Thelower chamber section 186 is shorter in length than the upper chambersection 185. The two cylindrical drying chamber sections 185, 186 againare releasably secured together by an array 102 b of circumferentiallyspaced quick disconnect fasteners 121 similar to those described above.The mounting ring 110 for this array 102 b of fasteners 121 is welded tothe upper cylindrical drying chamber section 185 adjacent the lower endthereof and the fasteners 121 of that array 102 b are oriented with thedraw hooks 122 downwardly positioned for engaging and retaining anunderside of a top outer radial flange 188 (FIGS. 1 and 2) of the lowercylindrical drying chamber section 186. Upon release of the two arrays102 a, 102 b of fasteners 121 affixing the lower cylindrical section 186to the upper cylindrical section 185 and the collection cone 18, thelower cylindrical section 186 can be removed, the lower standoff ringassembly 104 repositioned adjacent the bottom of the upper chambersection 185, and the liner 100 replaced with a shorter length liner. Theupper cylindrical dryer chamber section 185 can then be secured directlyonto the powder collection cone 18 with the lower standoff ring assembly104 therebetween by the fasteners 121 of the array 102 b which thenengage the outer annular flange 129 of the collection cone 18. Thismodification enables use of a substantially shorter length effectivedrying zone for further reducing heating requirements for smaller lotdrying.

It will be appreciated that additional cylindrical drying chambermodules or sections 186 could be added to further increase the effectivelength of the drying chamber 12. For increasing the quantity sprayedliquid into the drying chamber 12, whether or not increased in size, aplurality of electrostatic spray nozzle assemblies 16 can be provided inthe top cover 14, as depicted in FIGS. 19 and 20. The plurality of spraynozzle assemblies 16, which may be supplied from the common liquid andnitrogen supplies, preferably are supported in a circumferential spacedrelation to each other in respective, previously capped, amountingapertures 190 in the top cover 14 (FIG. 4). The then unused centralmounting aperture 192 (FIG. 20) may be appropriately capped or otherwiseclosed.

According to still another feature of this embodiment, the modular quickdisconnect components of the drying tower 11 further enables relocationof the electrostatic spray nozzle assembly 16 from a position on top ofthe drying chamber 12 for downward spraying to a position adjacent abottom of the drying chamber 12 for the upward direction of anelectrostatically charged liquid spray into the drying chamber 12. Tothis end, the spray nozzle assembly 16 may be removed from the top cover14 and secured in a bottom spray nozzle mounting support 195 (FIGS.21-24), which in this case is mounted within the upper cylindrical wallsection 155 of the powder collection cone 18 immediately adjacent thebottom of the drying chamber 12 for orienting the electrostatic spraynozzle assembly 16 for spraying charged spray pattern upwardly into thedrying chamber 12, as depicted in FIG. 21. The illustrated bottom nozzlemounting support 195, as depicted in FIGS. 22-24, includes a centralannular mounting hub 196 for supporting the spray nozzle assembly 16adjacent an upstream end which, in turn, is supported in the uppercylindrical section 155 of the powder collection cone 18 by a pluralityof radial mounting rods 198 made of a non-conductive material. Theradial mounting rods 198 each are secured to the cylindrical wallsection 155 by respective stainless steel screws 199 (FIG. 24) with arubber bonded sealing washing 200 between the head of the screw 199 andthe outer wall surface of the powder collection cone 18 and a scalingo-ring 201 is interposed between the outer end of each mounting rod 198and the inside wall surface of the powder collection cone section 18.Non-conductive Teflon or other plastic liquid and atomizing gas supplylines 205, 206 respectively connect radially outwardly to insulatedfittings 208, 209 by powder collection cone 18, which in turn areconnected to the atomizing air and liquid supply lines 151, 131. A highvoltage power cable 210 also connects radially with the nozzle assemblythrough an insulated fitting 211.

With the electrostatic spray nozzle assembly 16 mounted adjacent theunderside of the drying chamber 12, a central spray nozzle mountingaperture 192 in the cover 14 may be appropriately capped, as well as thegas inlet port 15. The powder collection cone 18 further has atangentially oriented drying gas inlet 215, which may be uncapped andconnected to the drying gas recirculation line 165, and the cover 14 inthis case has a pair of exhaust ports 216 which also may be uncapped forconnection to the heating gas return line.

With the spray nozzle assembly 16 mounted on the underside of the dryingchamber 12, electrostatically charged liquid spray particles directedupwardly into the drying chamber 12 are dried by drying gasses, which inthis case are tangentially directed through the bottom heating gas inlet215 and by heating atomizing gas from the spray nozzle assembly 16,which again both are dry inert gas, i.e. nitrogen.

Pursuant to this embodiment, the annular liner 100 in the drying chamber12 preferably is made of a filter media 100 b (FIG. 3B) for enabling thedrying gas to ultimately migrate through the filter media for exit outfrom the upper exhaust ports 216 in the cover 14 to the recirculationline 165 for recirculation, reheating, and redirection to the bottom gasinlet port 215, as explained above. The powder dried by the upwardlydirected drying gas and atomizing gas will ultimately float downwardlyinto and through the powder collection cone 18 into the collectionchamber 19, as described above, with only the finest particles beingfiltered by the filter media liner 100. The pneumatic liner shaker againmay be periodically actuated to prevent the accumulation of powder onthe liner 100.

From the foregoing, it can be seen that the processing tower can beeasily configured and operated in a variety of processing modes forparticular spray applications, as depicted in the table 220 in FIG. 25.The drying chamber length may be electively changed by adding orremoving the cylindrical dryer chamber section 186, the material of theliner may be selectively determined, such as non-permeable or permeable,the electrostatic spray nozzle orientation may be changed between topspraying downwardly or bottom spraying upwardly, and the processed gasflow direction can be changed between downward or upward directionsbased upon the desired configuration.

While in the foregoing embodiments, nitrogen or other inert drying gas,is introduced into the system as atomizing gas to the electrostaticspray nozzle assembly 16, alternatively, the nitrogen gas could beintroduced into the recirculating gas. In the spray dry system asdepicted in FIG. 25A, wherein parts similar to those described abovehave been given similar references numerals to those described above,nitrogen or other inert gas is introduced into the gas heater 169 from anitrogen injection line 169 a for direction to the drying chamber 100via the gas delivery and supply line 169 a and recirculation from thedrying chamber 100 through the condenser 170, and blower 168 asdescribed previously. In that embodiment, nitrogen gas can also besupplied to the electrostatic spray nozzle assembly 16 as atomizing gas,as described above, or air, or a combination of an inert gas and air,can be supplied to the electrostatic spray nozzle assembly 16 as theatomizing gas so long as it does not create a combustive atmospherewithin the drying chamber. Operation of the drying system depicted inFIG. 25A otherwise is the same as in previously described.

With reference to FIG. 25B, there is shown another alternativeembodiment drying system similar to that described above, except that apowder collection cone 18 a directs powder to a conventional cycloneseparator/filter bag housing 19 a in which dried product is dischargedfrom a lower outlet 19 b and exhaust air is directed from an upperexhaust port line 165 for recirculation through the condenser 170, theblower 168, drying gas heater 169 and the drying chamber 11. In FIG.25C, there is shown an alternative embodiment of drying system similarto that shown in FIG. 25B but with a fine powder recirculation line 19 cbetween the cyclone separator and filter bag housing 19 a and the upperend of the drying chamber 11. Dried fine particulates separated in thecyclone separator 19 a are recirculated through the fine powderrecirculation line 19 c to the drying chamber 11 for producing powershaving agglomerations of fine particles. Again, the system otherwiseoperates the same as previously described.

Referring now to FIG. 25D there is shown another alternative embodimentin the form of a fluidized bed powder drying system. The powder dryingsystem again has a cylindrical drying chamber 12 with a non-permeableliner 100 concentrically disposed therein and an electrostatic spraynozzle assembly 16 for directing electrostatically charged liquidparticles into the effective heating zone 127 defined by the liner 100as described above. In this case, a conically formed collectioncontainer section 18 b communicates powder from the drying chamber 12into a collection chamber 19 b through a fluid bed screen separator 19 cof a conventional type. In this embodiment, a plurality of fluid bedcylindrical filter elements 160 b, similar to those described inconnection with the embodiment of FIG. 11A, are supported from an uppertransverse plate 163 b which defines an exhaust plenum 164 b adjacent atop of the drying chamber 12. A blower 168 in this case draws air fromthe exhaust plenum 164 b from which powder and particulate matter hasbeen filtered out for direction via the line 165 through the condenser170 and heater 169, for reintroduction into the bottom collectionchamber 19 b and recirculation upwardly through the drying chamber 12.The filters 16 b again have reverse pulse air filter cleaning devices167 b of the type as disclosed in the referenced U.S. Pat. No.8,876,928, having respective air control valves 167 c for periodicallydirecting pressurized air to and through the filters 16 b for cleaningthe filters 16 b of accumulated powder.

While the non-permeable liner 100 of the foregoing embodiments,preferably is made of flexible non-conductive material, such as plastic,alternatively it could be made of a rigid plastic material, as depictedin FIG. 3D. In that case, appropriate non-conductive mounting standoffs100 d could be provided for securing the liner in concentric relationwithin the drying chamber 12. Alternatively, as depicted in FIG. 3C thepermeable liner can be made in part, such as one diametrical side, of apermeable filter material 100 b which allows air to flow through theliner for exhaust and in part, such as on an opposite diametric side, ofa non permeable material 100 a that prevents dried particles from beingdrawn into the liner.

As a further alternative embodiment, the illustrated spray dryer systemcan be easily modified, as depicted in FIG. 15A, for use in spraychilling of melted flow streams, such as waxes, hard waxes, andglycerides, into a cold gas stream to form solidified particles. Similaritems to those described above have been given similar referencenumerals. During spray chilling, a feedstock with a melting point,slightly above ambient conditions, is heated and placed in the holdingtank 130 which in this case is wrapped in an insulation 130 a. The feedstock is pumped to the atomizing nozzle 16 thru the feed line 131 usingthe pump 132. The molten feedstock again is atomized using compressedgas such as nitrogen 150. During spray chilling melted liquid feedstockmay or may not be electrostatically charged. In the latter case, theelectrode of the electrostatic spray nozzle assembly is deenergized.

During spray chilling, the atomizing gas heater 152 is turned off sothat cool atomizing gas is delivered to the atomizing nozzle 16. Duringthe spray chilling, the drying gas heater 169 also is turned offdelivering drying gas that has been cooled by the dehumidification coil170 a to the drying chamber 12 through the drying gas line 165. As theatomized droplets enter the drying gas zone 127 they solidify to formparticles that fall into the collection cone 18 and are collected in thecollection chamber 19 as the gas stream exits for recirculation. Theremovable liner 100 again aids in the cleaning of the dryer chambersince it can be removed and discarded. The insulating air gap 101prevents the drying chamber 12 from becoming cold enough forcondensation to form on the outside surface.

In carrying out still a further feature of this embodiment, the sprayingsystem 10 may operate using an automated fault recovery system thatallows for continued operation of the system in the event of a momentarycharge field breakdown in the drying chamber, while providing an alarmsignal in the event of continued electrical breakdown. A flowchart for amethod of operating a voltage generator fault recovery method for use inthe spraying system 10 is shown in FIG. 27. The illustrated method maybe operating in the form of a program or a set of computer executableinstructions that are carried out within the controller 133 (FIG. 15).In accordance with the illustrated embodiments, the method shown in FIG.26 includes activating or otherwise starting a liquid pump at 300 toprovide a pressurized supply of fluid to an injector inlet. At 302, averification of whether a voltage supply is active is carried out. Inthe event the voltage supply is determined to be inactive at 302, anerror message is provided at a machine interface at 304, and a voltagegenerator and the liquid pump are deactivated at 306 until a fault thatis present, which may have caused the voltage supply to not be active asdetermined at 302, has been rectified.

At times when the voltage supply is determined at 302 to be active, adelay of a predefined time, for example, 5 seconds, is used before theliquid pump is started at 308, and the liquid pump is run at 310 afterthe delay has expired. A check is performed at 312 for a short or an arcat 312 while the pump continues to run at 310. When a short or are isdetected at 312, an event counter and also a timer are maintained todetermine whether more than a predefined number of shorts or arcs, forexample, five, have been detected within a predefined period, forexample, 30 seconds. These checks are determined at 314 each time ashort or arc is detected at 312. When fewer than the predefined shortsor arcs occur within the predefined period, or even if a single short orare is detected, the liquid pump is stopped at 316, the voltagegenerator producing the voltage is reset by, for example, shutting downand restarting, at 318, and the liquid pump is restarted at 310 afterthe delay at 308, such that the system can remediate the fault thatcaused the spark or are and the system can continue operating. However,in the event more than the predefined number of sparks or arc occurwithin the predefined period at 314, an error message is generated at amachine interface at 320 and the system is placed into a standby mode bydeactivating the voltage generator and the liquid pump at 306.

In one aspect, therefore, the method of remediating a fault in anelectrostatic spray drying system includes starting a pump startupsequence, which entails first determining a state of the voltagegenerator and not allowing the liquid pump to turn on while the voltagegenerator has not yet activated. To accomplish this, in one embodiment,a time delay is used before the liquid pump is turned on, to permitsufficient time for the voltage generator to activate. The liquid pumpis then started, and the system continuously monitors for the presenceof a spark or an arc, for example, by monitoring the current drawn fromthe voltage generator, while the pump is operating. When a fault isdetected, the voltage generator turns off, as does the liquid pump, anddepending on the extent of the fault, the system automatically restartsor enters into a standby mode that requires the operator's attention andaction to restart the system.

Finally, in carrying out a further aspect of the present embodiment, thespray drying system 10 has a control which enables the charge to theliquid sprayed by the electrostatic spray nozzle assembly to beperiodically varied in a fashion that can induce a controlled andselective agglomeration of the sprayed particles for particular sprayapplications and ultimate usage of the dried product. In one embodiment,the selective or controlled agglomeration of the sprayed particles isaccomplished by varying the time and frequency of sprayer activation,for example, by use of a pulse width modulated (PWM) injector commandsignal, between high and low activation frequencies to produce sprayedparticles of different sizes that can result in a varying extent ofagglomeration. In another embodiment, the selective or controlledagglomeration of the sprayed particles may be accomplished by modulatingthe level of the voltage that is applied to electrostatically charge thesprayed fluid. For example, the voltage may be varied selectively in arange such as 0-30 kV. It is contemplated that for such voltagevariations, higher voltage applied to charge the fluid will act togenerally decrease the size of the droplets, thus decreasing dryingtime, and may further induce the carrier to migrate towards the outersurfaces of the droplets, thus improving encapsulation. Similarly, adecrease in the voltage applied may tend to increase the size of thedroplets, which may aid in agglomeration, especially in the presence ofsmaller droplets or particles.

Other embodiments contemplated that can selectively affect theagglomeration of the sprayed particles include selectively changing overtime, or pulsing between high and low predetermined values, variousother operating parameters of the system. In one embodiment, theatomizing gas pressure, the fluid delivery pressure, and the atomizinggas temperature may be varied to control or generally affect particlesize and also the drying time of the droplets. Additional embodimentsmay further include varying other parameters of the atomizing gas and/orthe drying air such as their respective absolute or relative moisturecontent, water activity, droplet or particle size and others. In oneparticular contemplated embodiment, the dew point temperature of theatomizing gas and the drying air are actively controlled, and in anotherembodiment, the volume or mass airflow of the atomizing gas and/or thedrying air are also actively controlled.

A flowchart for a method of modulating a pulse width in an electrostaticspray nozzle to selectively control the agglomeration of sprayedparticles is shown in FIG. 27. In accordance with one embodiment, at aninitiation of the process, a voltage generator is turned on at 322. Adetermination of whether a PWM control, which will selectively controlthe agglomeration, is active or desired is carried out at 324. When noPWM is desired or active, the process controls the system by controllingthe voltage generator to a voltage setpoint at 326, and the fluidinjector is operated normally. When PWM is desired or active, the systemalternates between a low PWM setpoint and a high PWM setpoint forpredefined periods and during a cycle time. In the illustratedembodiment, this is accomplished by controlling to the low PWM setpointat 328 for a low pulse duration time at 330. When the low pulse durationtime has expired, the system switches to a high PWM setpoint at 332until a high pulse duration time has expired at 334, and returns to 324to determine if a further PWM cycle is desired. While changes in the PWMsetpoint are discussed herein relative to the flowchart shown in FIG.27, it should be appreciated that other parameters may be modulated inaddition to, or instead of, the sprayer PWM. As discussed above, otherparameters that may be used include the level of voltage applied tocharge the liquid, the atomizing gas pressure, the liquid delivery rateand/or pressure, the atomizing gas temperature, the moisture content ofthe atomizing gas and/or drying air, and/or the volume or mass air flowof the atomizing gas and/or drying air.

In one aspect, therefore, the agglomeration of sprayed particles iscontrolled by varying the injection time of the sprayer. At highfrequencies, i.e., at a high PWM, the sprayer will open and close morerapidly producing smaller particles. At low frequencies, i.e., at thelow PWM, the sprayer will open and close more slowly producing largerparticles. As the larger and smaller particles make their way throughthe dryer in alternating layers, some will physically interact and bindtogether regardless of their repulsing electrical charges to produceagglomerates by collusion. The specific size of the larger and smallerparticles, and also the respective number of each particle size per unittime that are produced, can be controlled by the system by setting therespective high and low PWM setpoints, and also the duration for each,to suit each specific application.

In accordance with still a further feature, a plurality of powderprocessing towers 10 having drying chambers 11 and electrostatic spraynozzle assemblies 16 as described above, may be provided in a modulardesign, as depicted in FIGS. 28 and 29, with the powder discharging ontoa common conveyor system 340 or the like. In this case, a plurality ofprocessing towers 10 are provided in adjacent relation to each otheraround a common working platform 341 accessible to the top by astaircase 342, and having a control panel and operator interface 344located at an end thereof. The processing towers 10 in this case eachinclude a plurality of electrostatic spray nozzle assemblies 16. Asdepicted in FIG. 28, eight substantially identical processing towers 10are provided, in this case discharging powder onto a common powderconveyor 340, such as a screw feed, pneumatic, or other powder transfermeans, to a collection container.

Such a modular processing system has been found to have a number ofimportant advantages. At the outset, it is a scalable processing systemthat can be tailored to a users requirements, using common components,namely substantially identical processing powder processing towers 10.The system also can easily be expanded with additional modules, asdepicted in FIG. 30. The use of such a modular arrangement of processingtowers 10 also enables processing of greater quantities of powder withsmaller building height requirements (15-20 feet) as compared tostandard larger production spray dryer systems which are 40 feet andgreater in height and require special building layouts for installation.The modular design further permits isolation and service individualprocessing towers of the system without interrupting the operation ofother modules for maintenance during processing. The modular arrangementalso enables the system to be scaled for energy usage for particularuser production requirements. For example, five modules could be usedfor one processing requirement and only three used for another batch.

From the foregoing, it can be seen that a spray dryer system is providedthat is more efficient and versatile in operation. Due to enhanceddrying efficiency, the spray dryer system can be both smaller in sizeand more economical usage. The electrostatic spray system further iseffective for drying different product lots without cross-contaminationand is easily modifiable, both in size and processing techniques, forparticular spray applications. The spray drying system further is lesssusceptible to electrical malfunction and dangerous explosions from finepowder within the atmosphere of the drying chamber. The system furthercan be selectively operated to form particles that agglomerate into aform that better facilitates their subsequent usage. The system furtherhas an exhaust gas filtration system for more effectively andefficiently removing airborne particulate matter from drying gas exitingthe dryer and which includes automatic means for removing the buildup ofdried particulate matter on the filters which can impede operation andrequire costly maintenance. Yet, the system is relatively simple inconstruction and lends itself to economical manufacture.

1. A fluidized bed spray drying system for drying liquid into powdercomprising: an elongated body supported in an upright position; aclosure arrangement at opposite upper and lower ends of the elongatedbody for forming a drying chamber within said elongated body; a linerdisposed within said elongated body in spaced relation to an inner wallsurface of the elongated body for defining an internal drying zone withsaid elongated body; a spray nozzle assembly supported in one of theclosure arrangements; said spray nozzle assembly including a nozzle bodyhaving a liquid inlet for coupling to a supply of liquid, a dischargespray tip assembly at a downstream end for directing liquid to be driedinto said drying zone and an electrode for coupling to an electricalsource for electrically charging liquid passing through said spraynozzle assembly into said drying zone; said lower end closurearrangement including a powder collection chamber for collecting powderdried in said drying zone; said powder collection chamber having adrying gas inlet for introducing drying gas into said drying chamber fordrying liquid directed into the drying chamber into powder; said upperend closure arrangement having a plurality of filter elementscommunicating with an exhaust gas outlet for filtering drying gas bornepowder from drying gas exiting the drying chamber through said filterelements and the exhaust gas outlet; and said cylindrical filterelements each being closed at one end and having an opposite open axialend communicating with said exhaust gas outely such that drying gasexiting the drying chamber passes through a cylindrical side of thefilter element which restrains gas borne powder with drying gasproceeding through the cylindrical side of the filter element and thenout the open axial end to said exhaust gas outlet.
 2. The spray dryingsystem of claim 1 wherein a fluid bed screen separator is arrangedbetween the powder collection chamber and the remainder of the elongatedbody.
 3. The spray drying system of claim 1 wherein the plurality ofcylindrical filter elements are supported from a transverse plate in theupper end closure arrangement that defines at least a portion of anexhaust plenum communicating with the exhaust gas outlet.
 4. The spraydrying system of claim 3 in which said filter elements each aresupported in depending relation to said transverse plate with the openaxial end at an upper end communicating with said exhaust plenum suchthat drying gas passes through cylindrical sides of the filter elementsand exits the upper open axial ends of the filter elements into theexhaust plenum.
 5. The spray drying system of claim 1 including arecirculation conduit coupled between said exhaust gas outlet and thedrying gas inlet for reintroducing drying gas into the drying chamber.6. The spray drying system of claim 5 wherein the recirculation conduitdirects drying gas first through a condenser and then through a heateras gas is recirculated from the exhaust gas outlet to the drying gasinlet.
 7. The spray drying system of claim 1 in which said filterelement housing includes an outer cylindrical housing wall and an innercylindrical shroud surrounding said filter elements, said innercylindrical shroud and outer filter element cylindrical housing walldefining an annular drying gas passageway communicating between saiddrying chamber and said powder collection chamber.
 8. The spray dryingsystem of claim 1 including a conical collection container arrangedbetween the powder collection chamber and the remainder of the elongatedbody for directing powder into the powder collection chamber.
 9. Thespray drying system of claim 8 including a fluid bed screen separatorarranged between the powder collection chamber and the powder collectionchamber.
 10. The spray drying system of claim 1 in which said nozzlebody has an atomizing gas inlet for coupling to a pressurized gas supplyfor directing pressurized atomizing air through said nozzle body foratomizing electrostatically charged liquid discharging from thedischarge spray tip assembly.
 11. The spray drying system of claim 1 inwhich said filter elements each have a respective reverse gas pulsedirecting device cyclically operateable for directing pulses ofpressurized gas into an interior of the cylindrical filter element forremoving the buildup of powder on an outside cylindrical surfacethereof.
 12. The spray drying system of claim 11 in which each saidreverse gas pulse directing device includes an gas directing tube havinga discharge end centered above the open axial end of the cylindricalfilter element, and said gas direction tube of each gas pulse directingdevice having an upstream end coupled to a respective pressurizedcontrol valve.
 13. The spray drying system of claim 12 in which saidcontrol valve of each reverse gas pulse directing device has arespective gas pressure supply line coupled between the respectivecontrol valve and a common pressurized gas manifold chamber.
 14. Thespray drying system of claim 1 in which each said cylindrical filterelement has a respective reverse gas pulse filter cleaning device havinga selectively operable reverse gas pulse nozzle coupled to a pressurizedgas source for directing pressurized gas into the cylindrical filterelement for dislodging powder accumulated on an outside surface of thecylindrical filter element, a plunger mounted for movement between anopen position that permits the flow of drying gas through saidcylindrical filter element and axially through the open axial endcommunicating with the exhaust outlet and a closing position thatinterrupts and prevents the flow of drying gas from within thecollection chamber to said exhaust outlet, and said plunger beingmoveable from said open position to said closed position as an incidentto the direction of pressurized gas through said reverse pulse nozzlefor enabling pressurized gas from the reverse pulse nozzle to bedirected into the cylindrical filter element and outwardly through thecylindrical sides thereof without the flow of drying gas into saidexhaust chamber.
 15. The spray drying system of claim 14 in which eachsaid reverse gas pulse nozzle has a hollow construction through whichpressurized gas is directed, said reverse pulse gas nozzle having afirst portion disposed within an exhaust plenum and a second portiondisposed within and extending substantially the length of thecylindrical filter element, and said plunger being supported formovement along said first portion of said reverse pulse nozzle.
 16. Thespray drying system of claim 15 in which each said reverse gas pulsenozzle first portion is formed with a plurality of apertures forpermitting communication of pressurized gas from said reverse pulsenozzle and into said plunger cylinder for moving said plunger to saidclosing position, and said nozzle second portion being formed with aplurality of apertures smaller in size than the apertures in the firstportion for permitting the flow of pressurized air from said reversepulse nozzle into said cylindrical filter element and outwardlycylindrical sides thereof when said valve plunger is in said secondposition.
 17. A fluidized bed spray drying system for drying liquid intopowder comprising: an elongated body supported in an upright position; aclosure arrangement at opposite upper and lower ends of the elongatedbody for forming a drying chamber within said elongated body; a spraynozzle assembly supported in one of the closure arrangements; said spraynozzle assembly including a nozzle body having a liquid inlet forcoupling to a supply of liquid and a discharge spray tip assembly at adownstream end for directing liquid to be dried into said dryingchamber; said lower end closure arrangement including a powdercollection chamber for collecting powder dried in said drying zone; saidpowder collection chamber having a drying gas inlet for introducingdrying gas into said drying chamber for drying liquid directed into thedrying chamber into powder; said upper end closure arrangement having aplurality of filter elements communicating with an exhaust gas outletfor filtering drying gas borne powder from drying gas exiting the dryingchamber through said filter elements and the exhaust gas outlet; saidcylindrical filter elements each being closed at one end and having anopposite open axial end communicating with said exhaust gas outlet suchthat drying gas exiting the drying chamber passes through a cylindricalside of the filter element which restrains gas borne powder with dryinggas proceeding through the cylindrical side of the filter element andthen out the open axial end to said exhaust gas outlet; and arecirculation conduit coupled between said exhaust gas outlet and thedrying gas inlet for reintroducing drying gas into the drying chamber,wherein the recirculation conduit directs drying gas first through acondenser and then through a heater as gas is recirculated from theexhaust gas outlet to the drying gas inlet.
 18. The spray drying systemof claim 17 wherein a fluid bed screen separator is arranged between thepowder collection chamber and the remainder of the elongated body. 19.The spray drying system of claim 17 wherein the plurality of cylindricalfilter elements are supported from a transverse plate in the upper endclosure arrangement that defines at least a portion of an exhaust plenumcommunicating with the exhaust gas outlet.
 20. The spray drying systemof claim 19 in which said filter elements each are supported independing relation to said transverse plate with the open axial end atan upper end communicating with said exhaust plenum such that drying gaspasses through cylindrical sides of the filter elements and exits theupper open axial ends of the filter elements into the exhaust plenum.